The present invention relates to room temperature vulcanizable organopolysiloxane compositions having improved shelf stability and a reduced tendency to corrode copper metal. More particularly, the present invention relates to moisture curable organopolysiloxane compositions using a tin condensation catalyst having organo radicals attached to tin by carbon tin linkages and whose remaining valences are satisfied by an arylotriazolate group, for example, di(n-butyl)tin bis(benzotriazolate).
Prior to the present invention, as shown by Brown et al., U.S. Pat. No. 3,161,614, attempts were made to make stable room temperature vulcanizable (RTV) compositions employing a polyalkoxy end blocked polysiloxane and a monocarboxylic acid metal salt catalyst, such as dibutyltindilaurate. These compositions did not cure satisfactorily. Improved results were obtained by Beers, U.S. Pat. No. 4,100,129, assigned to the same assignee as the present invention, utilizing as a condensation catalyst, a silanol reactive organometallic ester having organo radicals attached to metal through metal-oxygen-carbon linkages. Experience has shown that in instances where silanol reactive organo tin compounds are used as RTV condensation catalysts which have organo radicals attached to tin by tin-oxygen-carbon linkages, the resulting moisture curable compositions are often unstable.
As utilized hereinafter, the term "stable" as applied to the one package polyalkoxy-terminated organopolysiloxane RTV's of the present invention means a moisture curable mixture capable of remaining substantially unchanged while excluded from atmospheric moisture and which cures to a tack-free elastomer after an extended shelf period. In addition, a stable RTV also means that the tack-free time exhibited by freshly mixed RTV ingredients under atmospheric conditions will be substantially the same as that exhibited by the same mixture of ingredients exposed to atmospheric moisture after having been held in a moisture resistant and moisture-free container for an extended shelf period at ambient conditions, or an equivalent period based on accelerated aging at an elevated temperature.
Further advances were achieved with the employment of silane scavengers for eliminating chemically combined hydroxy radicals, water, or methanol, as shown by White et al., U.S. Pat. No. 4,395,526, assigned to the same assignee as the present invention and incorporated herein by reference. However, the preparation of these silane scavengers, such as methyldimethoxy-(N-methylacetamide)silane often require special techniques and undesirable by-products can be generated during cure. Further improvements are shown by Dziark, U.S. Pat. No. 4,417,042 for scavengers for one component alkoxy functional RTV compositions and processes, assigned to the same assignee as the present invention and incorporated herein by reference.
Organic scavengers for trace amounts of water, methanol and silanol are shown by White et al., Serial No. 481,524, for One Package, Stable, Moisture Curable Alkoxyterminated Organopolysiloxane Compositions, filed Apr. 1, 1983, now Patent No. 4,472,551 assigned to the same assignee as the present invention and incorporated herein by reference. Additional scavenging techniques for chemically combined hydroxy functional radicals are shown by Lockhart in copending applications Ser. No. 481,529, now U.S. Pat. No. 4,499,230, Ser. No. 481,527, now U.S. Pat. No. 4,499,229, Ser. No. 481,528, now U.S. Pat. No. 4,477,625, and Ser. No. 481,530, now U.S. Pat. No. 4,467,063, filed concurrently on Apr. 1, 1983.
Although the above discussed techniques for improving the stability of room temperature vulcanizable organopolysiloxane compositions employing a tin condensation catalyst have been found to provide stable, substantially acid-free, curable organopolysiloxanes, a separate organic, inorganic, or organosilicon scavenger for hydroxy functional radicals is required.
The present invention is based on a discovery that stable room temperature vulcanizable compositions which also exhibit outstanding corrosion resistance to copper can be achieved by employing a tin condensation catalyst having the formula EQU (R).sub.2 Sn(Q).sub.2 ( 1)
where Q is a monovalent radical selected from a triazole having the formula, ##STR1## and an imidazole having the formula, ##STR2## where R is selected from C.sub.(1-18) monovalent hydrocarbon radicals and substituted C.sub.(1-18) monovalent hydrocarbon radicals, R.sup.1, R.sup.2 and R.sup.3 are selected from the same or different monovalent radicals selected from hydrogen and R radicals and X is divalent C.sub.(1-50) organic radical selected from hydrocarbon radicals and substituted hydrocarbon radicals.